An opposed piston two stroke diesel engine may have advantages over a four stroke diesel including reduced mechanical complexity, reduced displacement for equivalent power, and reduced fuel consumption. However, a four stroke diesel engine may provide useful engine braking to reduce or maintain vehicle speed when driver demand torque is low. The four stroke engine provides engine braking when exhaust manifold pressure is increased to a greater pressure than engine intake manifold pressure, thereby creating a positive pressure change in pressure across the engine (e.g., between the cylinder intake valves and exhaust valves). The positive pressure across the engine increases engine pumping work to provide engine braking. However, a two stroke engine requires intake manifold pressure to be greater than exhaust manifold pressure to ensure air flow through the engine. Further, engine pumping work of a two stroke engine is not affected by boosting a two-stroke engine. Therefore, engine braking from engine pumping work of a two stroke engine is not increased or decreased when the two stroke engine is boosted. However, engine braking may be desirable to control vehicle speed whether the vehicle includes a four stroke or two stroke engine. Therefore, it may be desirable to provide a way of engine braking for a two stroke opposed piston engine.
The inventor herein has recognized the above-mentioned disadvantages and has developed a two stroke diesel engine braking method, comprising: increasing engine braking torque of a two stroke engine without increasing engine pumping work via the mechanically driven supercharger in response to a request for engine braking; and supplying air to engine cylinders via the mechanically driven supercharger.
By adjusting flow through a mechanically driven supercharger, it may be possible to provide the technical result of providing engine braking via a two stroke engine without increasing engine pumping work. In particular, work performed by the mechanically driven supercharger may be adjusted via controlling flow through the mechanically driven supercharger. And, since the mechanically driven supercharger is part of the engine and coupled to the engine crankshaft, engine braking may be increased or decreased via adjusting flow through the mechanically driven supercharger. Flow through the mechanically driven supercharger may be adjusted via an exhaust throttle or vanes of a variable geometry turbocharger. In addition, positions of the exhaust valve and the turbocharger turbine vanes may be adjusted in proportion to a desired engine braking amount so that engine braking may be continuously variable.
The present description may provide several advantages. Specifically, the approach may allow a two stroke diesel engine to supply engine braking. Further, the amount or level of engine braking may be adjusted proportionately in response to an engine braking request. Further still, the approach may be realized with more than a single hardware configuration. Additionally, by not increasing engine pumping work while performing engine braking, it may be possible to more precisely control engine braking since changes in engine pumping work may not have to be determined to control engine braking.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.